<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .red{
      background-color: red;
    }
  </style>
</head>

<body>
  <div>
    <div id="test">test</div>
  </div>
  <div id="empty">
    <div class="div1"></div>
    <div class="div2"></div>
    <div class="div3"></div>
  </div>
  <div id="each">
    <div></div>
    <div></div>
    <div></div>
  </div>
  <script src="dom.js"></script>
  <script src="main.js"></script>
</body>

</html>